1. Field of the Invention
This invention relates generally to the field of carbon fiber reinforced metal-matrix composites and specifically to fiber coatings that enhance the wettability of the fibers by a molten metal and chemically bond with an alloying metal in the metal matrix.
2. Prior Art
Processes for manufacturing carbon or graphite-fiber-reinforced metal-matrix composites which have relatively high strength-to-weight and stiffness-to weight ratios have traditionally had the problem of graphite fiber resistance to wetting when immersed in molten baths of the metal-matrix material and/or degradation of the fibers during the course of said wetting. Because molten metal does not wet or bond to graphite fibers, it is impossible to achieve load transfer from the matrix to the fibers. What has been required then is a process whereby the fibers could be coated with a material that not only facilitates wetting, but also protects the fibers against chemical degradation during such processing. One of the prior art processes that has been used is chemical vapor deposition (CVD) of a thin film of titanium (Ti) and boron (B) on the fiber to facilitate the wetting, and alloying of (Ti-B) to the matrix metal to reduce migration of the coating as respectively described in U.S. Pat. No. 4,082,864 of Apr. 4, 1978 to Kendall et al, and U.S. Pat. No. 4,223,075 of Sept. 16, 1980 to Harrigan, et al. Such deposition, although a meritorious improvement over other prior art methods, is still relatively expensive and not always consistent as to results. Accordingly, there was a need for a process that would enhance the wettability of graphite/carbon fiber while disallowing degradation during the immersion in the molten bath of the metal matrix material.
This need was partially filled by my prior invention described in U.S. Pat. No. 4,376,803 wherein fibers were coated by a metal oxide derived from an organometallic solution which enhanced the ability of a metal to wet a fiber. That invention was particularly useful for the metal magnesium, but less useful for the metal copper. Accordingly, there was still a need for a process that would particularly enhance the wettability of copper with regards to such fibers.
U.S. Pat. No. 4,267,211 issued May 12, 1981 to Yajima et al teaches the coating of fibers with silicon carbide but does not recognize that if the matrix does not chemically react with the coated fibers then the bond is weak. Furthermore, Yajima does not recognize that the bond between the metal and the coated fibers can be strengthened by alloying the non-reactive base metal with a second reactive metal.